Remote control apparatus



April 11, 1944.

F. M. SCHMIDT ETAL REMOTE CONTROL APPARATUS Original Filed June 11, 1941 5 Sheets-Sheet l INVENTORS,

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F. M. SCHMIDT ETAL REMOTE CONTROL APPARATUS Original Filed June 11, 1941 [MLQ 3 Sheets-Sheet 2 Zr MYRTLE SHANDREW/A Mx.)

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REMOTE CONTROL APPARATUS Original Filed June 11, 1941 3 Sheets-Sheet 5 PIq. 3

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ORNEYS.

Patented Apr. 11, 1944 REMOTE CONTROL APPARATUS Francis M. Schmidt, North Tonawanda, N..Y.,

and Gerald G. Smith, deceased,

late of Kenmore, N. Y., by Myrtle Shandrew, admlnistratrix, Kenmore, N. Y., assignors to The Rudolph Wurlitzer Company, Cincinnati, Ohio Original application June 11, 1941, Serial No. 397,554. Divided and this application May 20, 1942, Serial No. 443,828

'1 Claim.

This invention relates to a remote control apparatus which is particularly adapted to the selective control of automatic record changing phonographs but may be used for other'purposes as well, and is a. division of our application Serial No. 397,554, filed June 11, 1941.

Certain features of the apparatus disclosed herelnare shown and claimed in co-pending application'of Charles J. Hull and Fred H. Osborne,

Serial No. 355,204, filed September 3, 1940.

' One object of the present invention is to provide apparatus-bymeans of which a controlled machinemay be operated from a remote station which is connected only through the power I mains which supply power for the controlled machine and for the remote station.

' Another object of the invention is to provide remote control apparatus of'this type which is able to discriminate accurately against spurious signals which might appear on the power lines and which might interfere with the operation of the controlled machine. For this purpose the controlling si'gnals'consist of a radio frequency carrier signalpower modulated by a series of audio frequency impulses. 'The number of such impulses in a series determines the selective operation of the controlled machine and the impulses preferably occur-at definitely timed intervals. Selectivity against spurious signals is obtained first by 1 accurate tuning of the sending and receiving apparatus for a' particular frequency of the carrierwave; second, by similar tuning for-audio frequency impulses and third, by wasting a predetermined number of impulses at the beginning,

of each series. Preferably at least two such impulses are wasted-that is, a series of at least three impulses is required to effect any operation of the controlled machine. While one or possibly by other apparatus. Apparatus to produce the necessary impulses to operate the machine must be'practically a duplicate of the authorized apaparatus and must be similarly tuned.

- Another means by which the apparatu discriminates against transient signals is by the f use of suitable slow acting apparatus at the receiver which prevents operation by transient im- Pulses 'of' short duration.

Another feature of the invention resides in particular manner'in which the radio frequency carrier is modulated. This arrangement permits power. modulation with a minimum number of tubes and parts- Other objects and features of the invention will be understood from the accompanying drawings and the following description and claim:

Fig. 1 is a diagram of electrical connections and apparatus illustrating a preferred form of remote control station. Fig. 2 is a similar diagram illustrating a preferred form' of receiving apparatus. Fig. '3 is a perspective view of certain mechanical parts of the receiving apparatus with the stationary framework thereof omitted to show moving parts in more detail. Fig. 4 is a fragmentary view partly in section of a portion of the apparatus shown in Fig. 3. Fig. 5' is a diagram showing inconventional form the relation of the remote station, the receiver and a controlled machine to the commercial power circuits by means of which they are supplied and over which controlling signals are transmitted;

The invention is best adapted for use in a home or commercial establishment which is provided with the usual electrical wiring having suitable outlet sockets to which'th controlled machine and the remote control apparatus may be connected by the usual socket plugs. For use in a commercial application such as a restaurant, the control will ordinarily b dependent upon the insertion of a coin. Obviously for home use the coin control may be omitted. InFig. 5 there is shown a pair of conductors 10 which may be considered as the distributory conductors of a commercial power company leading to the premises on which the invention is to be 'us'ed. Connected to the conductors l0 there'is shown the usual local transfor'mer ll having a secondary winding connected to power mains l2 supplying the individual customer of the power company. Suitable cutout switches and overloadpro'tection, not shown, may be assumed to be connected between the transformer II and the mains l2. Appliance outlet sockets l3-are connected to the mains I2 in the usual manner and may be placed at any desirable position on th premises. Adjacent any one of the outlets I3 theremay'be installed a signal transmitter [4 having a cord l5 and socket plug l6 which may be connected to the socket l3. 'A signal receiver ll having a cord I8 and plug l9 may be similarly connected to another of the sockets IS. The machine to be controlled is shown in Fig. 5 in the form of an automatic record changing phonograph 2fl'connected to the signal receiver by a-cord 2|. If desired, the receiver I! may be placed within the cabinet of the phonograph -20.

Signal transmitter For coin operation the signal transmitter it may be supplied with a coin slot 22 of any well known form adapted to receive a coin of a given denomination.- Within the receiver there is provided a switch 23 (Fig. 1) which is momentarily closed upon the receipt of a coin in the coin slot ously returned to said position.

22. Many different forms of coin receiver and coin operated switches which may be used are known in the art and it is therefore unnecessary to describe the same in detail.

There is also provided a multi-point manual selector switch 24 which may be operated by a suitable knob 25 on the face of the transnritter l4. The switch 24 has a plurality of contact points 26 each connected by one of a group of conductors 21 with a corresponding point 29 on a motor driven multi-point switch 29. Other electrical apparatus within the transmitter l4 includes an electromagnetic relay 38 adapted when energized to close a series of normally open switches 3|, 32 and 33 and a motor 34 adapted to operate the multi-point switch 29 and to rotate a series of cams 35, 36 and 31. The mechanical connections of the motor to the switch 29 and the respective cams are indicated schematically in Fig. 1 by broken lines and it is to be understood that these connections are such that each of the cams and the motor driven switch make one revolution in a definite period of time. The cams 35, 36 and 31 operate switches 38, 39 and 40, respectively. Said cams and switches and the switch 29 are shown in Fig. 1 in their initial idle position. Each cycle of motor operation starts with the parts in this idle position and continues until all of said parts are simultane- There are also provided electron discharge tubes 4|, 42 and 43. Tube 4| is shown as a standard pentode tube and is used as a generator of radio frequency energy. Tube 42 is a twin triode tube. One of the triode elements is used as a radio frequency amplifier and modulator and the other as an audio frequency oscillator. Obviously two standard triode tubes could be used in place of the single tube 42. Tube 43 is shown as a diode tube connected as a half wave rectifier to supply the necessary D. C. plate voltages for tubes 4| and 42. In practice it is advantageous to combine the elements of tubes 41 and 43 in a single tube but separate tubes are illustrated in the drawings for the sake of simplicity.

Porter for operating the transmitter is supplied from the plug I6 to a pair of line conductors 44 and *5, in one of which there may be placed a cutout switch 46. A transformer 41 has its primary winding connected to the line conductors 44 and 45 and its secondary winding arranged to supply current for the rectifier tube 43 and for a winding of transformer 41 is grounded and the opposite terminal is connected to the anode 58 of the rectifier tube 43. The cathode of said tube is connected to a distributory conductor 52 which is maintained thereby at a suitable potential above ground and supplies the necessary D. C. potential for the plate circuits of tubes 4! and 42. A condenser 53 connected between the cathode and ground serves to smooth out the D. C. voltage.

The cathodes of the several tubes may be heated by heating elements connected to suitable taps on the primary or secondary windings of the transformer 41 in a conventional manner.

The remaining electrical apparatus illustrated in Fig. 1 may best be described in connection with the circuits in which they are included.

In the operation of the transmitter the switch 24 i first set on one of the points 26 by means of the knob 25. Each of the points 26 corresponds to an operation Of the controlled machine and in'the case of a selective record changing phonograph each of said points corr sponds t one of the records carried in the magazine of said phonograph. Obviously, as many such contact points as are needed may be used. In the drawings, for sake of simplicity, only eight are shown. The setting of the switch 24 may be indicated by a suitable scale visible to the operator and corresponding with a suitable index of record titles. r

When the switch 24 has been properly set, a coin is deposited and switch 23 momentarily closed to complete a circuit from the line conductor 44 through switch 23, the winding of relay 30 and a resistance 49 to the line conductor 45. The consequent actuation of the relay 30 closes switch 3| which is in parallel with switch 23 and thus retains the relay in energized condition after switch 23 has been opened.

The operation of relay 3!! also closes switch 32 and completes a circuit through said switch to start the motor 34. The first movement of the motor 34 operates the cam 35 to close switch 38 and short circuit the switch 32. The motor thus continues to operate until cam 35 has made a complete revolution and the parts have returned to idle position even though switch 32 is opened at a later time in the cycle of operation. The operation of motor 34 also actuates cam 36 to open switch 39 and break a normally closed circuit for the lamp 48. Said circuit leads from ground through switch 39, a resistor 54, lamp 48 and a portion of the secondary winding of transformer 41 back to ground. Switch 39 is not again closed until cam 36 has returned to idle position and thus the signal lamp 48 when lighted indicates that the motor 34 is not in operation.

The operation of motor 34 also rotates the finger 55 of the multi-point switch 29 in the direction of the arrow. In this rotation the finger 55 successively engages the contact points 28. When said finger reaches the point 28 connected to the point 26 on which the switch 24 is set, a shunt circuit i closed around the winding of the relay 30 and said relay is thereby deenerized. The provision of the resistor 49 prevents the formation of a dead short across the line conductors and thus serves as an overload protection. It will be apparent that the length of time during which the relay 38 is energized depends entirely upon the setting of the switch 24 and that after said relay i deenergized the finger 55 is returned to its normal idle position since the motor 34 continues to operate until cam 35 opens switch 38. During th operation of the motor the signa1 lamp 48 is not burning. When said lamp is again lighted at the end of a cycle of motor operation, it indicates that the apparatus is ready for the receipt of another coin.

The actuation of the relay 38 also closes switch 33 to start the operation of the radio frequency oscillator tube 4!. Said tube i provided with a conventional anode-cathode circuit leading from the D. C. distributory conductor 52, through inductance 56 and tuning condenser 51 in parallel to the anode 58 and thence through the cathode 58 and switch 33 to ground. The grid-cathode circuit leads from cathode 59 to control grid 68 through resistor 6| and the parallel path formed by inductance 62 and condenser 63. Inductances 56 and 62 are coupled to give the necessary feedback for oscillation and the frequency of oscillation is controlled by the tuning condenser 51. Preferably oscillations of the order of 250 k. c. are used. Since switch 33 is included in the anode-cathode circuit radio frequency energy is .03 to eliminate harmonics.

enerated in the circuits of said tube only when relay 30 is energized and switch 33 is closed.

The radio frequency energy generated in the tube 4| is amplified and power modulated by the tube 42 and associated circuits. In tube 42 the audio oscillator section consists of cathode 84, control grid 65 and. anode 68. The radio frequency section of the tube consists of cathode 61, grid 68 and anode 89. The two cathodes 84 and 6'! are connected together and are connected to ground through the lower half of a variable inductance I which is thus common to the cathode circuits of both sections Of the tube. A condenser Il serves as a radio frequency by-pass for the cathode circuits. The grid 85 is connected to the cathodes through a resistor I2 and to the inductance I0 through a resistor 13 and the switch 40. A condenser I4 is shunted across the inductance I0 to complete the audio frequency tuned circuit. The plate 86 is directly connected to the D. C. distributory conductor 52. The grid 68 is coupled to the grid of tube 4I through a condenser I5 and resistor 16. Inductance 11 serves as a radio frequency choke between grid 58 and thecathode circuits. Anode 69 is connected to the D. C. distributory conductor 52 through condenser I8, variable condenser I9 and inductance 80 all connected in parallel and together forming a radio frequency tank.

In the electrical connections just described, the inductance I0 and condenser I4 form the tuned circuit of the audio frequency section of the tube 42. The grid 85 receives the necessary energy for oscillation from the tuned circuit, only when the switch 40 is closed. The lower portion of the inductance 10 also forms a part of the cathode circuit of the radio frequency section of the tube 42, so that the potential of the cathode 61 is affected by the oscillating current in the inductance I0. Thus the inductance I0 serves the dual purpose of producing oscillation and controlling the potential of the cathode 61 to modulate the radio frequency energy.

Radio frequency energy from tube H is fed to the grid 68 through the condenser and resistor I6 and is amplified, modulated and impressed upon the tank circuit 'I8I980 by the radio section of tube 42. The switch 40 is operated by the cam 31, and said cam is so formed that the switch 40 is alternately opened and closed at regular intervals. The modulation of the radio frequency is thus given the form of a series of power impulses. the frequency of which is determined by the tuning of the resonant circuit 10-14. Preferably, said circuit is tuned to a frequency of the order of 400 cycles per second.

The inductance 80 is coupled with an inductance 8|, connected in series with an inductance 82 and a condenser 83. The inductances 8| and 82, and the condenser 83 form a link circuit in which currents induced by the coupling with inductance 8| may be tuned by the condenser The inductance 82 is closely coupled with an inductance 84 and loosely coupled with an inductance 85, and said coupling induces corresponding high frequency energy therein. One terminal of each of the inductances 84 and 85 is connected to the line conductor 44, and the opposite terminals of said inductances may be selectively connected to the line conductor 45 by a switch 88 connected to the last mentioned line conductor through a condenser 81.

By means of the connections just described, the amplified and modulated radio frequency output of tube 42 is impressed upon the line conduc tors 44 and 45 by either one of the inductances 84 and 85, the particular one of said inductance to be used being chosen by manual operation of the switch 88, and the choice depending upon the impedance of the external circuit between the remotestation and the local station and consequent strength of signal required.

The cam 37 and the switch 20 are both operated by themotor 34 and the audio frequency impulse produced by the operation of switch 40 may thus be accurately timed with relation to the movement of switch 29. It will be noted that in the movement of switch 28 from the initial idle position, the finger 55 travels some distance before the first of the contact points 28 is reached. Preferably, the cam 31 is so shaped that it produces three audio impulses during this time. Thus three audio impulses are generated and impressed upon the line conductors before the finger 55 reaches the first oi" the contact points 28. During the movement of the finger 55, between each of the succeeding contact points, an additiona1 audio frequency impulse is produced.

I Thus, if the switch 24 is set on the contact point 26 corresponding to the first of contact points 28, a series of three audio frequency impulses is transmitted before the relay 30 is deenergized to stop the production of radio frequency oscillation. Similarly, the setting of the switch 24 onany one of the other contact'points 28, results in the production of a series of impulses of correspondingly greater number.

Receiver Power for operating the receiver I? and the controlled machine 20 is supplied from the plug I9 to a pair of power lines I00 and IOI in one winding of the transformer 103 is connected to a conductor I0! which is grounded through a resistor I08. The rectifier tube I04 thus serves as a full wave rectifier to maintain a suitable D. C. potential difference between conductors E05 and I0'I. The resistances I08 and I08 are so chosen that conductor I05 carries a suitable potential for the plate circuits of the several tubes used in the receiver and the conductor I01 carries a negative potential.

The electrical apparatus of the receiver also includes a radio frequency transformer I08, a pentode tube II 0 used for radio frequency amplification, a radio frequency transformer IN, a tube II2 having a diode rectifier section and a triocle amplifier section used for audio frequency amplification and a similar tube I I3. Other electrical elements shown in Fig, 2 will be described in connection with the circuit in which they.

are included.

The primary winding of the transformer I00 is connected to the line conductors I00 and IN through condensers I I4 and I I5 adapted to transmit radio frequency energy but to block the usual 60 cycle commercial current. Thus the modulated radio frequency signals generated in the transmitting apparatus are conducted from the transmitter I4 through the line conductors i2 5 and line conductors I00 and I film the trans-= former. parallel with the secondary windings of the transformer I09.and said signals induce corresponding currents in the secondary winding of said trans- A tuning condenser H6 is connected in former I09 to complete a resonant circuit which may be tuned to the radio frequency of the incoming signals. The resulting signal is impressed on the controlgrid II1.of tube II 0. The cathode H8 of tube H is connected to ground rthrough a conventional blazing resistor I I0 and condenser primary winding of transformer III.

The secondary winding of transformer III is provided with a tuning condenser I23 in parallel therewith to complete a tuned secondary circuit, one terminal of which is connected to the anode I24of the rectifier sectionof tubeI I2. The opposite terminal of said tuned circuit is connected to the cathode I25 of said tube through resistors I26, I21 and I28. The D. C. voltage produced in the circuit just described by operation of the rectifier section of tube II2 appears across the resistor I26, I21 and I28 and is applied to the control grid circuit oftube'IIO through a conductor I29 and a filter network consisting of a resistor I30 and condensers I3I and I32 to provide automatic volume control.

The control grid I33 of the amplifier section. of tube H2 is connected through a coupling condenser I34 to a point in the rectifier circuit just described where suitable variations in voltage are obtained for the operation of said amplifier section. Said grid is connected to ground through a conventional grid coupling resistor I34A. The

cathode I35 is connected to. cathode I25 and is biased to ground in a conventional manner. The anode I36 is connected to the D- C. distributory conductor I through a resistance I31. The connections just described complete a conventional stage of audio frequency amplification as a result of which a pulsating current of audio frequency corresponding to the transmitted impulses isgenerated in the circuit of anode I36.

The anode I36 is coupled by means of a condenser I38 to a circuit consisting of a variable inductance I40 and condenser I4I connected in parallel and a high frequency choke I45 and resistor I46 connected inseries therewith and connected to the negative D. C. conductor I01. In this circuit the inductance I40 and condenser I4I form a tuned portion which may be adjusted to the particular frequency of the signal impulses. Voltages due to the signal impulses appear across the tuned portion of the circuit while voltages due to transient higher frequency energy appear across the choke I45 since its impedance to high frequency current is high as compared to that for lower frequency currents. I

A rectifier circuit consisting of the rectifier anode I39, cathode I44, resistor I42 and condenser I43 is connected in parallel with the tuned portion of the circuit just described, but the connection isexclusive of the choke I45. Current flow in the rectifier circuit is thus controlled by the low frequency voltages across-the tuned portion and is substantially unaffected by higher frequency voltages across the choke I45. This arrangement therefore provides an additional .second section of tube lI-3.

lower end of said resistor is connected through choke I45 and resistor I46 to the negative D. C. conductor I01 and the opposite end of said resistor is connected to the control grid I41 of the The cathode I48 of said second section is grounded and the anode I ISI is connected through the winding of a relay I50 to the positive D. C. conductor I05. Because of the negative potential of the conductor I01 which is impressed upon the grid I41 when no current flows. in the rectifier circuit, the second section of tube 3 is normally biased to cutoff and no anode current is drawn. During the receipt of a signal impulse, the voltage appearing across the resistor I42 raises the potential of the control grid I41 sufficiently to permit current fiow in the anode circuit to energize the relay I50. Thus, said relayis momentarily energized in-response to each of the signal impulses.

The relay I50 preferably is adjusted for relatively slow action by use of a copper core or other well known means so that transient impulses of short duration cannot energize the relay. However, the speed of operation of the relay is not reduced sufficiently to prevent a distinct actuation for each signal impulse and a distinct release of the relay between the impulses.

Referring now to Figs. 3 and 4, there is illustrated therein certain mechanical apparatus forming a part of the receiver and actuated by operation of the solenoid I50. In said figure only .movable parts of the apparatus are shown and it will be understood that said parts may be supported on any suitable stationary struc- I ture. Said apparatus includes a shaft I carryrotated in the direction of the arrow. The shaft I60 also carries a ratchet wheel I63 and is urged in the clockwise direction by a torsion spring I64, one end of which is secured to said shaft and the opposite .end to a part of the stationary structure. a stationary position and is adapted to attract an armature I66 which is pivotally mounted on a pin I61. A finger I68 is pivotally mounted by means of a pin I69 on the armature I66 and is held against a stop pin I10 by a tension spring I 1|, the end of which is anchored to a stationary portion of the apparatus. The finger I68 is in position to engage the teeth of the ratchet wheel I63 and to move the ratchet wheel a distance corresponding to one tooth each time the magnet I65 is energized. A pawl I12 is mounted on a pivot pin I 13 and may be held in engagement with the teeth of the ratchet wheel I63 by a tension spring I14. Said pawl is adapted to hold the ratchet wheel in the positions in which it is placed by operation of the magnet I65.

A lever arm I16 is adapted to engage the tail of the pawl I13 and'to disengage the same from the teeth of the ratchet wheel. Said lever arm is pivotally mounted within a time delay device I11 which may be of a common commercial form, the details of which form no part of the present An electromagnet I65 is mounted in V invention. It is suflicient to say that the device has an'action somewhat similar to that of a dashpot. That is, the lever arm I16 'may be rapidly lifted by a small force in opposition to the action of a tension spring I18. When the lifting force is withdrawn, the spring I18 returns the lever I16 to its lower position but the time delay device I11 operates to slow the'return movement to a predetermined slow speed which may be adjusted as desired. For lifting the lever arm I18 there is provided a vertical rod I19, the upper end of which is pivoted to the lever arm I16 and the lower end of which is reduced and extends through a loosely fitting opening in the armature I66, as shown in Fig. 4.

In the normal idle position ,of the apparatus, the lever arm I16 is held in its lower position by the spring I18 and engages the pawl I12 to free the same from the ratchet wheel I63. Said ratchet wheel carries a stop pin I80 engaging a suitable stationary stop I8I which holds the ratchet wheel in an initial idle position when the pawl I12 is disengaged therefrom. In this position the contact finger I6I is out of engagement with the contact points I62 and is positioned at a sufficient distance from the first of said contact points so that three actuations of the magnet I65 are required before said contact finger reaches said first contract point. Each actuation of the magnet I65 moves the ratchet wheel I63 and the contact finger I6I one step in the counterclockwise direction. The first such actuation causes the lever arm I16 to be lifted free of the pawl I12 and permits said pawl to hold the ratchet wheel. After each actuation of magnet I65 the slow downward movement of the lever I16 is begun but each succeeding actuation returns said lever to its upper position. Thus. if a series of actuations of the magnet I 65 occurs with sufficient frequency the time delay device I11 prevents the arm I16 from freeing the pawl I12 between actuations. At the end of a series of such actuations, the lever arm I16 moves slowly downward and eventually engages the pawl I 12, releasing the same from the ratchet wheel and permitting the ratchet wheel to return to normal idle position.

Referring again to Fig. 2, the relay I50 actuates a switch I62 to close a circuit from line conductor I through magnet I65 to the line conductor IN. The switch I62 is closed each time the relay I50 is energized. Thus the magnet I 65 acts as a repeater for the relay I50 and is momentarily actuated in response to each signal imnulse received from the transmitter. The

lever I16 in its uppermost position is adapted to I engage and operate a pair of switches I83 and I84, the switch I83 being closed. and the switch I84 being opened when so engaged. Said switches are preferably adjusted so that in the upward and downward movement of the lever arm I16 each of said switches is closed before the other is opened. The switch I83 when closed completes a circuit from the power lines I00 and I0 I for a relay I85. Said relay when actuated closes a switch I86.

In the operation of this portion of the apparatus. the first si nal im u se ece ved cau an actuation of magnet I65 to lift the lever I16 to close switch I 83 and thereafter open switch I84. The operation of switch I 83 energizes the relay I85. The movement of the lever I16 in the upward direction is relatively rapid so that switch I84 is opened before relay I85 has closed switch for operation, it is not always necessary that an especially slow acting relay be used for operation of switch I86. However, a slow acting relay may be used if necessary since it is desirable to open switch I84 before switch I86 is closed. At the' end of a series of signal impulses, the contact finger I6I has been placed by operation of magnet I65 on one of the contact points I62. In this connection it is to be noted that the initial position of said contact finger is sufllciently far from the first of the contact points I62 so that a series of three impulses is required before said finger reaches the first of said contact points. Thus each of the contact points I62 corresponds to one of the contact points 26 and the point I62 selected by operation of magnet I 65 is determined by the setting of switch 24.

The cessation of signal impulses permits the lever I16 to move slowly downwardly. In this movement the switch I 84 is closed considerably before switch I83 is opened. The operation of switch I84 completes a circuit from line conductor I00-through switch I84 and switch I86 to the contact finger I6I and thence from the selected contact point I62 to one of a series of electromagnets I15, each of which has its opposite terminal connected to the line conductor IOI. At the same time, a circuit is completed through the switches I84 and I 86 for an electromagnet I58. The electromagnets I58 and I15 form part of a controlled machine which may be of the type disclosed in Wilcox Patent No. 2,002,236 and the magnets I58 and I15 may correspond to the magnets I58 and I15 in said Wilcox patent. In that patent each of the magnets I15 controls the selection of a predetermined record and the magnet I 58 initiates one operation of the machine. For selection of the record and initiation of the operation only momentary actuations of the magnets I58 and I15 are required. As the downward movement of lever I 16 continues, switch I63 is opened to deenergize magnet I85. Switch I86 is thereby opened to break the circuits of the magnet I58 and the particular magnet I15 which is energized.

From the foregoing specification it will be seen that the invention provides an impulse type of remote control apparatus peculiarly discrimina-' tory against stray signals and therefore well suited to the transmission of its. signals over commercial power lines. The invention has been described in one of its preferred forms, the details of which may be varied between wide limits without departing from the scope of the invention as defined by the appended claim.

The invention claimed is: In a remote control receiver adapted to receive signals in the form of a high frequency carrier modulated by lower frequency power impulses, the sub-combination of a parallel tuned circuit tuned to the low frequency of said power impulses, a high frequency choke, connections applying demodulated signal energy across said tuned circuit and said choke in series, a rectifier circuit connected in parallel with said tuned circuit exclusive of said choke, and means utilizing current flow in said rectifier circuit to control operation of said receiver.

FRANCIS M. SCHMIDT. MYRTLE SHANDREW, Administratriz of the Estate of Gerald G. Smith,

Deceased. 

